Fundamental features of microbial cellulose utilization are examined at successively higher levels of aggregation encompassing the structure and composition of cellulosic biomass, taxonomic diversity, cellulase enzyme systems, molecular biology of cellulase enzymes, physiology of cellulolytic microorganisms, ecological aspects of cellulase-degrading communities, and rate-limiting factors in nature. The methodological basis for studying microbial cellulose utilization is considered relative to quantification of cells and enzymes in the presence of solid substrates as well as apparatus and analysis for cellulose-grown continuous cultures. Quantitative description of cellulose hydrolysis is addressed with respect to adsorption of cellulase enzymes, rates of enzymatic hydrolysis, bioenergetics of microbial cellulose utilization, kinetics of microbial cellulose utilization, and contrasting features compared to soluble substrate kinetics. A biological perspective on processing cellulosic biomass is presented, including features of pretreated substrates and alternative process configurations. Organism development is considered for "consolidated bioprocessing" (CBP), in which the production of cellulolytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products occur in one step. Two organism development strategies for CBP are examined: (i) improve product yield and tolerance in microorganisms able to utilize cellulose, or (ii) express a heterologous system for cellulose hydrolysis and utilization in microorganisms that exhibit high product yield and tolerance. A concluding discussion identifies unresolved issues pertaining to microbial cellulose utilization, suggests approaches by which such issues might be resolved, and contrasts a microbially oriented cellulose hydrolysis paradigm to the more conventional enzymatically oriented paradigm in both fundamental and applied contexts.

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Microbial cellulose utilization: fundamentals and biotechnology.

Despite an increased knowledge of microbial xylanolytic systems in the past few years, further studies are required to achieve a complete understanding of the mechanism of xylan degradation by microorganisms and their enzymes. The enzyme system used by microbes for the metabolism of xylan is the most important tool for investigating the use of the second most abundant polysaccharide (xylan) in nature. Recent studies on microbial xylanolytic systems have generally focussed on induction of enzyme production under different conditions, purification, characterization, molecular cloning and expression, and use of enzyme predominantly for pulp bleaching. Rationale approaches to achieve these goals require a detailed knowledge of the regulatory mechanism governing enzyme production. This review will focus on complex xylan structure and the microbial enzyme complex involved in its complete breakdown, studies on xylanase regulation and production and their potential industrial applications, with special reference to biobleaching.

Microbial xylanases and their industrial applications: a review.

CONTENTS I . Introduction . 11. Factors which influence microbial biomass . . . ( I ) Soil chemical factors . . . . . . . ( a ) Carbon and nitrogen limitation . . . . ( b ) Residue and nutrient amendment . . . (c) Influence of plants . . . . . . ( d ) Soil pH . . . . . . . . (e) Heavy metals and pesticides . . . . (2) Soil physical factors . . . . . . . ( a ) Soil texture and structure ( b ) Soil moisture and temperature (c) Seasonal fluctuations . . . . . . 111. Global distribution of microbial biomass . . . ( I ) Relationship with soil chemical factors and macroclimate

A comparative assessment of factors which influence microbial biomass carbon and nitrogen levels in soil

http://www.dzumenvis.nic.in/Biodegradation/pdf/Biodegradation%20of%20lignin.pdf

Biodegradation of lignin in a compost environment: a review

The aim of the present work was to provide a synopsis of the scientific literature concerning the effects of different tree spe- cies on soil and to quantify the effect of common European temperate forest species on soil fertility. The scientific literature dealing with the tree species effect on soil has been reviewed. The composition of forest overstory has an impact on the chemical, physical and biolo- gical characteristics of soil. This impact was highest in the topsoil. Different tree species had significantly different effects on water ba- lance and microclimate. The physical characteristics of soils also were modified depending on the overstory species, probably through modifications of the soil fauna. The rates of organic matter mineralization and nitrification seem to be dependent on tree species. A coni- ferous species, Picea abies, had negative input-output budgets for some nutrients, such as Ca and Mg. This species promoted a higher soil acidification and a decrease in pH. Thus, it should not be planted in very poor soils in areas affected by acidic atmospheric deposi- tions. Nevertheless, the effect of the canopy species on soil fertility was rarely significant enough to promote forest decline. The impact of a tree species on soil fertility varied depending on the type of bedrock, climate and forest management. forest soils / tree species / fertility / sustainability / resiliency

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Impact of several common tree species of European temperate forests on soil fertility

Six biodegradative actinomycete strains were grown on a dimeric model lignin compound of the β-aryl ether type. Although only two strains, Thermomonospora mesophila and Streptomyces badius, utilized the compound as a carbon and energy source and produced substantial amounts of monomeric products, all of the strains could demethylate the substrate and oxidize Cα on the phenylpropane side-chain. Streptomyces sp. EC1 produced small amounts of aromatic acids and unidentified lignin-derived products when grown on straw. This organism also produced cell-bound demethylase requiring H2O2 and Mn2+, protocatechuate 3,4-dioxygenase and β-carboxymuconate decarboxylase activity in response to growth on low-molecular-mass aromatic compounds but not lignocellulose or its polysaccharide components. Extracellular peroxidase and catalase activity were detected in all of the strains. These data are used to propose a scheme by which actinomycete attack of the lignin component of plant biomass can be envisaged.

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Towards elucidation of the lignin degradation pathway in actinomycetes

A Streptomyces sp. isolated from compost degraded the hemicellulose fraction of straw efficiently but apparently not native cellulose. Ball-milled straw induced endoglucanase, β-glucosidase, β-xylanase and β-xylosidase. Carboxymethylcellulose, cellotetraose and cellotriose induced cellulolytic enzymes specifically whereas cellobiose acted as inducer for β-glucosidase only. Cellotriose and cellotetraose induced β-glucosidase, but only partially induced endoglucanase. Hemicellulose (in the form of xylan) and xylobiose induced only β-xylanase and β-xylosidase. Kraft lignin and syringic acid induced β-xylanase and endoglucanase but not the other enzymes. 3,4-Dimethoxycinnamic acid slightly induced β-xylanase whereas 3,5-dimethoxy-4-hydroxycinnamic acid specifically induced endoglucanase. Neither veratric acid nor vanillic and ferulic acids induced any of the cellulolytic or hemicellulolytic enzymes. Enzyme production was subject to a form of carbon catabolite repression. Endoglucanase and β-xylanase were excreted into the culture medium. Four protein components, one acidic (pI 5.2) and three basic (pI 8.15, 8.45 and 8.65) exhibited β-xylanase activity. Two acidic components (pI 3.55 and 3.75) displayed endoglucanase activity.

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Regulation of the production of hemicellulolytic and cellulolytic enzymes by a Streptomyces sp. growing on lignocellulose.

Actinomycetes grown on wheat straw solubilized a lignocarbohydrate fraction which could be recovered by acid precipitation. Further characterization of this product (APPL) during growth of Streptomyces sp. strain EC1 revealed an increase in carboxylic acid and phenolic hydroxyl content, suggesting progressive modification. This was also observed in dioxane-extracted lignin fractions of degraded straw, and some similarity was further suggested by comparative infrared spectroscopy. However, the molecular weight profile of APPL was relatively constant during growth of Streptomyces sp. strain EC1 on straw, while analysis of the dioxane-extracted lignin fractions appeared to show fragmentation followed by repolymerization. Lignocarbohydrate solubilization could be monitored in all cultures by routine assay of APPL-associated protein, which accounted for up to 20% of the extracellular culture protein in some cases. Interestingly, this protein fraction was found to include active hydrolytic and oxidative enzymes involved in the degradation of lignocellulose, and specific enzyme activities were often increased in the acid-insoluble fractions of culture supernatants. This was particularly important for peroxidase and veratryl oxidase activities, which could be readily detected in the acid-precipitable lignocarbohydrate complex but were virtually undetectable in untreated culture supernatants.

Lignocarbohydrate Solubilization from Straw by Actinomycetes

Twenty Belgian agricultural soils, 16 of which had been organically cultivated, were examined for their biochemical and microbiological properties. In spite of the very different nature of the characteristics studied, close relationships were found between soil respiration and glucose mineralization rates, biomass-C as measured by the fumigation-incubation method, and several enzyme activities, namely FDA-hydrolase, alkaline phosphatase and dehydrogenase. Correlation coefficients between urease activity and other biological measurements were always found to be endowed with a negative sign. Moreover, factor analysis of the data showed that some physico-chemical characteristics such as soil organic C, total N, clay content and CEC were closely related to most of the biological measurements, while pH and sand content were not. Two procedures for the determination of dehydrogenase activity and two methods of calculation of biomass-C were also compared.

Factor analysis of the relationships between several physico-chemical and microbiological characteristics of some Belgian agricultural soils

Population changes in cellulolytic microflora were studied during composting of cattle manure. Six bacterial and nine actinomycetes species were isolated. Among the isolates, two actinomycetes, Micromonospora chalcae and Pseudonocardia thermophila, were cellulolytic strains which were numerically dominant and might therefore play a notable role in the degradation of cellulose in cattle manure. Fungi were practically absent during the process, but two cellulose-degrading bacterial species, Sporocytophaga myxococcoides and Cytophaga hutchinsonii, appeared to coexist in equilibrium with actinomycetes during the maturation phase.

Bernard Godden

Papers

Towards elucidation of the lignin degradation pathway in actinomycetes

Regulation of the production of hemicellulolytic and cellulolytic enzymes by a Streptomyces sp. growing on lignocellulose.

Lignocarbohydrate Solubilization from Straw by Actinomycetes

Factor analysis of the relationships between several physico-chemical and microbiological characteristics of some Belgian agricultural soils

Identification and evolution of the cellulolytic microflora present during composting of cattle manure: On the role of actinomycetes sp